Electric vehicles may have a battery and an electric drive unit for propulsion. The motor of the electric drive unit may be used as a regenerative brake; that is, it may be used as a generator to convert kinetic energy into electrical energy. It is desired to use the electrical energy provided by the electric drive unit to charge the battery.
However, in case of failure at high speeds of the electric vehicle and especially when the battery is nearly empty, large currents may flow into the battery. This may lead to large braking torques on one or more wheels of the electric vehicle which may lead to dangerous situations on slippery roads or in curves. Further, charging the battery with too high current may result in a fire or damage or destroy the battery, especially when the battery is already fully charged, too hot or too cold.
To prevent an uncontrolled charge of the battery, the maximum voltage of the motor may be chosen to be smaller than a minimum voltage of the battery. However, a larger current that is required in this case to provide the same power level may lead to heavier motors and larger control electronics for the electric motor, which may increase cost, space requirements and weight and reduce the electrical efficiency of the electric drive unit.